The invention relates to a radial piston pump in which balancing of the drive shaft eccentric and modifying the flow characteristics of the incoming fluid are implemented in an improved manner.
A radial piston pump of the generic type is disclosed by DE 32 31 878 C1. Such radial piston pumps, also referred to as bottom inlet radial piston pumps, have an inlet chamber in which there is arranged an eccentric which may be driven in a rotating manner for driving at least one piston. Furthermore, this radial piston pump has an inlet controller which opens or closes a connection between the inlet chamber and cylinder bore, depending on the piston position. Also arranged concentrically on the drive shaft bearing the eccentric is a disk that influences the intake stream. The diameter of the disk is selected such that there is a relatively small gap between the wall bounding the inlet chamber radially and the disk, so that a restrictor gap is formed -as viewed over the entire circumference of the disk.
U.S. Pat. No. 5,207,771 A discloses a radial piston pump which has balancing elements which are intended to compensate for imbalance caused by the eccentric. However, this known pump does not have a bottom inlet, which means that the eccentric and the balance weight are not arranged in the chamber which also forms the inlet chamber.
It is therefore an object of the invention to specify a radial piston pump of the type mentioned at the beginning in which exerting an influence on the inlet medium flow and balancing are implemented in a simple manner.
This object is achieved by a radial piston pump which has an inlet chamber comprising an inlet connection and an eccentric which can be driven in a rotating manner, arranged within the inlet chamber, for drive al least one piston of the radial piston-pump. In addition, it has a cylinder bore guiding the piston and an inlet controller which opens or closes a connection between the inlet chamber and the cylinder bore, depending on the piston position. According to the invention, the radial piston pump is distinguished by a balancing element for the eccentric, which rotates synchronously with the eccentric in the inlet chamber, whereby the balancing element is so arranged in the inlet chamber and/or its contour is so designed that a hydraulic resistance is formed between the inlet connection and the inlet controller, or the flow of medium to the inlet controller is unaffected. Surprisingly, it has been shown that, in order to exert an influence on the inlet medium flow, it is not necessary to use a circular disk, as proposed in DE 32 31 878 C1 mentioned above. Surprisingly, it has also been shown that a balancing element which does not form a circulating sealing gap with the wall of the inlet chamber permits an influence to be exerted on the inlet medium flow, so that the delivery characteristic of the radial piston pump can be varied. Depending on how the balancing element is arranged in the inlet chamber, the medium flow reaching the inlet controller can be restricted or can flow substantially unimpeded. If for example, the distance between the balancing element and the inlet controller and/or the inlet connection is chosen to be relatively small, a falling delivery characteristic can be achieved. On the other hand, if this distance is chosen to be sufficiently large, the medium flow reaching the inlet controller is substantially unaffected. The radial piston pump according to the invention therefore has, if necessary, a virtually unchanged delivery characteristic, but provides the advantage of compensating for the imbalance caused by the eccentric. As mentioned above, however, tho medium flow reaching the inlet controller can also be influenced by the contour of the balancing element. For example, provision can be made for the balancing element to taper in the radial direction, in order in the region of the inlet controller and/or the inlet connection to have a greater distance from the latter, so that as a result the medium flow is unaffected.
In a particularly preferred exemplary embodiment, the radial piston pump is designed to be inlet-restricted. Inlet-restricted radial piston pumps provide the advantage that, up to a specific speed of the drive shaft or of the eccentric, they have a rising delivery characteristic and, from this specific speed, also referred to as the limiting speed they have a horizontal delivery characteristic. In order not to lose this advantageous effect, provision is made, in particular in inlet-throttled radial piston pumps, for the balancing element to be arranged in the inlet chamber and/or for its contour to be so designed that the medium flow reaching the inlet controller is substantially unaffected. It is therefore possible, by using the balancing element according to the invention, to provide a bottom-inlet, inlet-restricted radial piston pump which has very low or no vibration and nevertheless has an unaffected delivery characteristic, that is to say above the predefinable limiting speed, substantially has a horizontal delivery characteristic. This radial piston pump is used in particular to supply a hydraulic system which actively influences the chassis of a motor vehicle.
A preferred exemplary embodiment is distinguished by the fact that the balancing element has a chamfer on its side facing the inlet controller, so that the thickness of the balancing element decreases radially outward. It has been shown that a balancing element designed in this way substantially does not affect the inlet medium flow to the inlet controller. In one exemplary embodiment, provision is made for the balancing element to comprise a disk segment. Alternatively, provision can be made for a disk to be provided which arranged with its mid-axis offset in relation to the eccentric. The balancing element therefore has a mass element which is associated with the eccentric in such a way that the unbalance caused by the eccentric is compensated.
In a preferred exemplary embodiment, provision is made for the eccentric and the balancing element to be arranged on a drive shaft which turns or rotates in the inlet chamber. Provision can be made for the eccentric to be formed in one piece with the drive shaft. In this case, the mid-axis of the balancing element does not coincide with the longitudinal axis of the drive shaft.
In order to achieve dynamic balancing, provision is made for a second balancing element to rotate synchronously with the eccentric. The two balancing elements are so oriented with respect to the eccentric that during the rotation of the drive shaft a couple is formed which compensates for the imbalance orienting from the eccentric, the two balancing elements being so arranged and so formed with respect to their mass that tilting moments caused by imbalance outside the mid-plane of the eccentric are also compensated.
According to one exemplary embodiment, at least one ofthe two balancing elements can be fitted to the drive shaft. In other words, at least one of the two balancing elements is pushed onto the drive shaft, the balancing element having an aperture whose internal diameter is so chosen that the balancing element is held firmly on the drive shaft.
According to another exemplary embodiment, provision is made for one of the two balancing elements to be formed in one piece with the drive shaft and for the other balancing element to be able to be fitted to the drive shaft. These configurations are provided in particular when the eccentric has a DU bush and a steel bush, which are pushed onto the eccentric contour. The steel bush co-operates with the piston crown of the at least one piston. The fact that a balancing element can be fitted to the drive shaft means that this preferably hardened steel bush and the inner DU bush can be pushed onto the eccentric first, so that the balancing element can then be fitted to the drive shaft. Here, the balancing elements are fitted to the drive shaft in such a way that the steel bush and the DU bush cannot slip off the eccentric.
According to a development of the invention, provision is made for the first balancing element to have a hub through which the drive shaft passes, the disk segment protruding from the hub. Instead of the disk segment, a circular disk can also be provided. This disk or the disk segment is used as a balance weight, which has an offset with respect to the mid-axis of the hub.
The axial length of the balancing element is particularly preferably dimensioned such that it bears with its one end on the side surface of the eccentric and with its other end on a wall bounding the inlet chamber. As a result, the drive shaft is fixed axially. A separate thrust disk can therefore be omitted.
In an advantageous development, the drive shaft passes through this wall bounding the inlet chamber and, with its free end, co-operate with a rotor of a second pump, in particular a vane pump. The drive shaft therefore drives both the radial piston pump and the second pump.
One exemplary embodiment is distinguished by the fact that the balancing element has, on its side facing the wall of the inlet chamber, a recess which is oriented radially outward and which forms a lubrication groove. The balancing element therefore serves simultaneously as a thrust disk, as it is known, a film of lubricant being formed between the balancing element and the wall bounding the inlet chamber.
In a preferred exemplary embodiment, provision is made for the inlet controller to comprise a control edge located in the opening area of the cylinder bore and at least one aperture located in the piston wall. The inlet controller is therefore preferably located in the inlet chamber. Depending on the piston position, this aperture is covered or opened by the control edge, so that the medium can be taken in via this aperture and therefore enters the cylinder, in order to be forced out of the cylinder again during a further piston movement.
Further refinements emerge from the subclaims.